The present invention concerns a system for withdrawing body fluid from a part of the body, especially the finger pad. Body fluids are primarily withdrawn for a subsequent analysis in order to diagnose diseases or to monitor the metabolic state of a patient. Such a withdrawal is carried out especially by diabetics in order to determine the blood sugar concentration. The aim of such a blood-sugar check that is usually carried out several times daily is to avoid hypoglycaemic states as well as hyperglycaemic states. In the case of a hypoglycaemia the patient can fall into a coma and even die since the brain is no longer adequately supplied with glucose. In contrast hyperglycaemic states can lead to long-term side-effects such as blindness, gangrenes and such like.
Consequently a frequent monitoring of the blood sugar level is an undisputed necessity. It is therefore obvious that there is an urgent need for sampling systems which are easy to operate by the user and are above all largely free of pain.
Already blood sampling systems have been known for some time in the prior art which allow the patient or hospital staff to carry out a withdrawal in a simple manner. A device suitable for this is for example the commercially available Softclix whose manner of operation is described in U.S. Pat. No. 5,318,584. This device provides an adjustment means for the depth to which a lancet is inserted into the tissue. Hence the patient can select the minimum puncture depth which enables a just sufficient quantity of blood to be obtained for a subsequent analysis and thus keep the incision pain very low. After the patient has produced a skin opening by piercing, he has to massage or press his finger in order to draw sufficient blood from the puncture wound especially with small puncture depths. This operation which is frequently referred to as “milking” by diabetics can hitherto only be avoided when the puncture is very deep and correspondingly unpleasant for the patient and can lead to major scarring on the sensitive finger tips. Devices known in the prior art attempt to stimulate the outflow of blood by applying a vacuum but this has proven to be not efficient.
Devices are also known in the prior art in which a so-called stimulator with a ring depresses the skin surface surrounding an incision site. Such a device for obtaining interstitial liquid is described for example in U.S. Pat. No. 5,582,184. The ring used to depress the skin surface is made of a rigid material. Only small amounts of fluid can be obtained with the device that are not adequate for commercial analytical systems.
Another device is known from U.S. Pat. No. 5,857,983 in which a syringe is inserted into the skin surface and the skin surface surrounding the site of incision is repeatedly depressed using a so-called stimulator in order to press body fluid into the syringe. Like the above-mentioned document a rigid ring is used in this device to depress the skin surface. The amounts of body fluid that can be obtained with this device are small and thus inadequate for conventional analytical systems.
Blood sampling devices are also described in the U.S. Pat. No. 5,951,493 which operate with a stimulator like the above-mentioned US patent. In addition a device is described in FIGS. 15 to 17 in which the area of the device that is used to press against a body surface is provided with levers (104) which laterally press together a part of the body while the device is pressed against the body surface. The devices described in this patent are in particular intended for withdrawing body fluids from other sites than the finger pad. In addition the document shows that the transport of body fluid onto the skin surface is achieved by repeated pressing of the device.
A device is known from the document U.S. Pat. No. 3,626,929 in which a finger is clamped before blood withdrawal between a lever and a finger support. The finger support is moved by a motor in order to result in a massaging proximal to the incision site. For the withdrawal the user's finger is pressed against a flexible cap in which needles and a fluid channel are located. A disadvantage of this device is that the needles for the withdrawal remain in the body and that in this state the finger support is moved. This results in the movement of the needles in the finger which usually leads to considerable pain. In addition it is extremely unlikely that blood will emerge while there is a needle in the finger so that the channel is closed by the needle. A collecting container is shown in FIGS. 11 and 12 which has a flexible pressure-application region. However, due to the shape of the pressure-application region which widens conically towards the finger there is no conversion of a primary pressure-application movement into a lateral movement which squeezes the sampling region together.
The object of the present invention was to provide a system for withdrawing body fluid which, using small puncture depths, yields an adequate amount of body fluid, in particular blood. An additional object of the invention was to provide a system which can be easily operated and has a simple construction. Simplicity in this sense means in particular that the number of operating steps is as small as possible.
A further object of the invention is in particular to simplify blood withdrawal from the finger pad and in doing so take into account different finger sizes and different puncture sites on the finger tip.
Consequently the present invention concerns a system for withdrawing body fluid from a part of the body in particular a finger pad comprising the following elements:                a compression unit against which a body part is pressed in a primary direction and partially converts the applied pressure into a movement in a secondary direction with a component perpendicular to the primary direction such that the internal pressure is increased in a region of said body part,        a perforation device, in particular a lancet or needle to produce a body opening in the region of the increased internal pressure,        wherein the compression unit has a pressure-application region made of a deformable material.        
The invention additionally includes a system for stimulating the outflow of body fluid from a body part, a process for stimulating outflow of body fluid and a process for withdrawing body fluid.
Use of the compression unit according to the invention enables the above-mentioned milking movement to be simulated in a simple and convenient manner for the user in order to squeeze out blood from the incision site. The compression unit not only yields larger quantities of body fluid than is the case with the compression devices of the prior art but the compression and withdrawal process is also considerably more pleasant for the patient. This is due to the fact that the compression unit fits snugly around the body part, in particular a finger. A further contributing factor is that the compression unit enables adequate quantities of body fluid to be obtained even with very small puncture depths.
An additional very important advantage of the present invention is that use of a compression unit with a pressure-application region made of deformable material enables body fluid to be withdrawn with the compression unit from body parts of various shape in a reliable and pleasant manner. In particular it easily and reliably enables withdrawal from fingers of different sizes. In addition the deformable material compensates for differences in the shape of the pressed body part (finger tip versus side of the finger).
The system according to the invention can be used particularly advantageously to obtain capillary blood from the finger pad. In addition it is also possible to withdraw blood or interstitial fluid from other body parts such as the arm.
An essential element of the system is the compression unit which results in the body part being squeezed together not only in the direction of the primary applied pressure but also results in the applied pressure being at least partially diverted such that a squeezing occurs with components of force transverse to the primary direction of pressure-application. As a result the region of the body part from which the withdrawal is to take place is pressed together laterally. The mode of action of this advantageous compression is elucidated later on the basis of the embodiments. The compression unit produces an increase of the internal pressure in a region of the body part. This region of increased internal pressure is adjacent to the region on which the applied pressure acts, or is surrounded by the region of applied pressure. A perforation device can now be used to perforate the region of increased internal pressure and remove body fluid.
The compression unit comprises a pressure-application region made of deformable material. On the one hand such a material makes the withdrawal process more pleasant for the user and, on the other hand, it also enables an easier adaptation to the various shapes and sizes of the body parts. Deformable plastics such as elastomers, rubbers and such like can for example be used as materials for the pressure-application region. The pressure-application region is preferably ring-shaped.
This represents a technically significant difference to the device described in FIGS. 15 to 16 of U.S. Pat. No. 5,951,493. In the device of the prior art an arrangement of separate lever arms is used to laterally press together the body surface. This has a number of disadvantages. As a result of the distance between the lever arms, the lateral squeezing of the skin surface is incomplete since areas remain untouched between the lever arms. Furthermore in the worst case the skin can get stuck between the lever arm while they move together. Finally it should be noted that the device of the prior art is neither designed nor suitable for fitting snugly to body surfaces of various sizes and shapes. The device is primarily intended to withdraw body fluid from a region of the arm which is less curved compared to the finger pad. The said problems can be avoided by using a pressure-application region made of a deformable material which preferably has a ring shape.
The system for removing body fluid additionally has a perforation device to produce a body opening. Such a perforation device can be a lancet or needle.
In the case of a lancet it is preferably completely removed from the tissue after the incision such that body fluid emerging from the site of incision is accessible. In the case of a needle it can remain at the maximum puncture depth in order to extract body fluid from this depth or it can be withdrawn until it reaches the skin surface in order to take up liquid from this position.
The perforation device can be preferably guided onto the body surface through an opening in the compression unit or the pressure-application region. In order to achieve various depths of incision to allow for various skin types and also to account for the required quantities of blood, it is advantageous to have a variable puncture depth. In order to achieve a defined (and optionally preset) puncture depth it has proven to be particularly advantageous to arrange the perforation device such that it can be displaced relative to the compression unit. This displaceability comprises two aspects which can also be combined. In the first aspect the perforation device is spring loaded relative to the compression unit such that a front face or a stop on the perforation device elastically rests against the body surface when the body part is pressed against the compression unit. The compressive force of the perforation device on the body surface is preferably in the range of 1 to 5 N and is preferably ca. 2 N. If greater compressive forces are used there is a danger that body fluid in the region of the increased internal pressure will be pressed out of this region.
The second aspect i.e. the relative displacement of the perforation device and compression unit concerns a movement of the perforation device into a perforation position and movement away from this position in order to create space to take up body fluid by means of a receiving device. This aspect is particularly important for an integrated system which can be used for blood withdrawal as well as analysis.
In advantageous embodiments of the invention the system for withdrawing body fluid is integrated into an analytical system. Such analytical systems are well-known in the prior art. For example analytical systems named ACCUCHECK PLUS® AND ACCUCHECK ADVANTAGE® are commercially available. As a rule analytical systems which are designed for consumers use disposable test elements which, after contact with a sample liquid, yield a signal which depends on the analyte concentration. In the field of blood sugar measurement optical test elements are used in which the reaction of glucose with a test chemistry leads to a change in colour as well as electrochemical test elements in which an enzymatic conversion of glucose enables an amperometric or potentiometric analysis. The test elements can be advantageously designed such that they actively take up body fluid (e.g. by means of a capillary gap).
The system according to the invention simplifies the integration of a withdrawal unit with an analytical system or for the first time makes an integration possible. As already stated it is customary in the prior art to manually press out the body fluid after producing a skin opening which means that the patient has to remove the body part from the withdrawal device. In contrast a system according to the present invention enables the patient to press the body part against the deformable compression unit and to leave it there in this compressed state to produce a skin opening as well as for the withdrawal. Hence a stronger degree of automation is possible in which the patient only has to press against the compression unit and all subsequent steps up to the read-out of the analytical result can proceed automatically.
Hence an integration of the perforation device and analytical system not only advantageously relates to a spatial integration but also to a process integration which avoids operating steps by the user. Correspondingly such a system also advantageously has a control unit which controls coodinatively activation of the withdrawal device, the withdrawal of body fluid and the transport of body fluid to the analytical system and the analysis.